Topic: '75 CB550, no power after parking and coming back out to the bike...short?

[mj1176]

Hey guys. Hopped on my 550 to head up the street real quick, no issues, but when I came back out of the store to start the bike again less than five minutes later, I get no power when I turn the key to "on." Checked and replaced fuses, no luck. Wasn't fun walking it home. I've never had electrical issues before and today is a very rainy humid day, so I'm thinking maybe it's possible some condensation or rain just got into somewhere it shouldn't have and is causing a short? I'm hoping it'll just start again when it drys out tomorrow but I've never heard of this happening and it's my daily driver, so I'm trying to eliminate any possible answers I might be missing before I commit to testing every connection between the ignition and the battery. Really hoping to not have to chase it down.

Thanks

[BomberMann650]

Test the battery and inspect the connections.  The key switch could be suspect too.
Look along the wiring harness for anywhere you could have a break in insulation.

Git to work on it and you might find your problem

[Scott S]

 Or the kill switch took a crap.

[mj1176]

99% your battery connections are loose, either at the battery, or at the frame ground. Probably riding it caused enough vibration to jar it loose enough not to spark after the key.

I just checked everything and they seem to be tight and making proper contact... still no power. But my battery ground wire is pretty old and crusty, is it possible the moisture today just finally did it in? How would I check to see if that wire's dead with a meter, just check if the negative battery terminal gets continuity to the frame?

Or the kill switch took a crap.

How do I determine that?

The key switch could be suspect too.


Git to work on it and you might find your problem

Now that you mention this, I do remember a couple times when I've put the key in and turned it to the On position and gotten no lights for a second. It's only happened once or twice and I got power as soon as I moved the key a little again but it would always start. How do I check the key switch itself?

[mj1176]

Getting antsy so I decided to pull the meter out tonight instead of waiting until tomorrow to see if it starts when the bike is dry. 12.36v at the battery so not quite fully charged but that should be more than enough to power the head/tail/idiot lights right? I'm stumped. Really hoping I can locate the gremlin tonight or early tomorrow morning, or I'm gonna have a rough day with no transportation.

[mj1176]

@cal with key on, battery voltage reads 12.36v, same as with key in off position. As far as the other test, pardon my ignorance, but I'm testing resistance, correct?

[mj1176]

Yes.
Interesting that you see no voltage drop with key ON, even a little? That would tell me either loose battery ground or key switch is not activating.

No voltage drop at all when I turn the key to on, checked the battery ground connection and it's solid. Resistance between the negative post and frame/motor is .2-.3 ohms. I'm starting to thing it's the switch too; if that's the case all I need to do to test it is pull it and measure for continuity across red and black when the key is in the on position right?

[markreimer]

I think you can jump the bike by removing the switch at it's four pin connector, and using two test wires to connect the two sets of wires in an X shape. As in top left to bottom right, top right to bottom left.

I can't recall the colors, I just remember bypassing the ignition on one of cb's that way and realizing how easy it would be to hotwire and steal it


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[mj1176]

Not really looking to hotwire it, if it is the switch I'll try the method in TT's switch contact point repair thread and start from there. It's just a rainy day here in Austin and I'm dragging my feet about getting outside to pull the switch and test it. I'll report back in a couple hours.

[markreimer]

Not really looking to hotwire it, if it is the switch I'll try the method in TT's switch contact point repair thread and start from there. It's just a rainy day here in Austin and I'm dragging my feet about getting outside to pull the switch and test it. I'll report back in a couple hours.

Yea I only suggested it as a way to pinpoint if your issue was the switch. I wouldn't suggest driving it that way!


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[mj1176]

It might actually be easier than getting the switch out... I tried to find a way to do it without removing the headlight or gauge cluster and I couldnt do it. Might be easier to try to unclip the harness connection and jump it. But if it starts then I know it's the switch and I need to pull it anyway...guess it's off with the gauge cluster tomorrow morning. Determined to get this fixed and enjoy the good weather forecast for tomorrow.

[mj1176]

@calj737 same results in second position, no idiot lights or power. I pulled the switch just now and tested continuity across the prongs that correspond with the red and black wires with the key in the on position but got nothing. I found a replacement switch locally so I'm going to swap them and see if that does it.

[mj1176]

It was the switch.  I pulled it, no continuity for the ignition prongs that go to red/black on the harness, no continuity or resistance reading to any of the prongs but the tail light one when the key is in the parking light position. I grabbed another ignition switch from a shop up the street and got it in the bike, now it starts up no problem. Just for #$%*s and giggles I opened up the old switch to see how bad it was and try to clean it per the TT guide so I'd have a spare. Here's a photo of pre-cleaning:

 

I cleaned it and reassembled but still still nothing. One of the points seems to have had the plastic melted up around it preventing contact with the other plates. I'd love to know how it failed but I guess 42 years of wear and corrosion does funky things to materials. Thanks for all your help, y'all.

[BomberMann650]

Yeah that's pretty fugly.

Good news, replacements are available.

[mj1176]

Luckily a shop up the street had one of the Emgo replacements so I'm good to go

[mj1176]

Not so. Emgo won't go for long. They are very poor quality switches and will likely leave you stranded soon enough (again). You can use a relay to help with reducing the amperage running through it and prolong its life and increase its reliability.

Hmm...good to know. What kind of relay do I need to run and where do I install it?